The invention relates to a regulator circuit for controlling the cooling and heating of automotive vehicles, and consists generally of an input amplifier supplied with signals proportional to the external temperature, and the internal temperature of the vehicle, and the desired temperature, the output signal of this amplifier regulating the heating system, and, by way of a second amplifier, the cooling system.
A regulator circuit of this general type is disclosed in published German Application No. 29 52 210 in which a differential amplifier is provided which receives the weighted control signals of an internal temperature sensor and a desired value setpoint control. The circuit regulates the heat exchanger of the heater by way of a change-over switch and a servo member. At the same time, the output signal of this differential amplifier is transmitted via an isolated amplifier and regulates the clutch of the compressor pertaining to the cooling system by way of a series of additional functional elements, including a limiter, a weighting circuit, a threshold switch, and a switching stage. Such a regulating circuit can also control additional functional elements of an air conditioning unit, such as a fresh air/circulated air flap.
With any such air conditioning system, switch-over must be provided from heating operation to cooling operation. The output signal of the input amplifier can be utilized for switch-over. Once this output signal falls below a certain value, switch-over is performed from heating operation to cooling operation in the conventional manner. This procedure has the drawback that the same desired value is set for the transition point of the cooling system independently of how this desired value was formed from the input variables of the input amplifier. The desired value may be given to the cooling system too high for the instantaneously ambient outside temperature. If the outside temperature is low during switch-over from heating to cooling operation and the cooling system is set to a desired value that is too large, the interior of the vehicle is cooled off excessively. As a reaction, the desired value rises again, effects cutoff of the cooling system, and activates the heating system. Subsequently, the desired value again falls below the transition point so that the cooling system is reactivated. Thus, oscillation results around the transition point between heating and cooling. This behavior is found to be uncomfortable by the occupants of the vehicle and requires increased energy consumption due to the constant activation and deactivation of the heating and cooling systems.
It is an object of the invention to provide a regulator circuit for controlling the cooling and heating power wherein oscillation around the transition point between heating and cooling is prevented. This object has been attained by providing that, in a regulator circuit of the above-discussed type, the second amplifier arranged behind the input amplifier, is additionally supplied with the signal proportional to the outside temperature. This results in the instantaneous external temperature being introduced into the cooling control system as the desired value at the transition point. Thus, when a low outside temperature exists and the system is heating, after the transition point has been passed through, cooling will either not commence or will commence only to a very small extent. Thereby, excessive cooling of the vehicle interior is prevented and oscillation between heating and cooling around the transition point is avoided. Since the cooling power will not become excessively high, a rather stable condition is attained.
It is advantageous to connect the input amplifier and the second amplifier as a summing amplifier. The temperature sensors employed can simply be negative temperature coefficient (NTC) thermistors. It is also possible to apply the signal proportional to the external temperature to an input of the second amplifier by way of a weighting resistor. The effect of the outside temperature on the output signal of the second amplifier can thus be set arbitrarily.
The resistor values pertaining to the summing circuits of the input amplifier and the second amplifier can advantageously be selected so that the cooling power regulation commences when the heating power regulation has reached the value zero. As a result, only a portion of the air conditioning system is always in operation--either the heating system or the cooling system.
However, it is also possible to design the heating range and the cooling range to be overlapping. In this case, a condition can occur wherein the heating system as well as the cooling system are in operation. This measure is called "counter heating" or "reheating" and serves for drying the air passing into the interior of the vehicle. For example, the aforementioned published application describes such a reheater, although this device must be activated manually, or activated by way of an additional switch, for instance, by a moisture probe. In this invention, it is possible to select the resistor values pertaining to the summing circuits of the input amplifier and of the second amplifier so that cooling power regulation starts at an early point in time when the heating power regulation has not as yet reached the value zero. This step leads to an overlapping between the cooling power regulation and the heating power regulation, and thus to an automatic start of reheating. The transition range wherein heating and cooling are carried out simultaneously is automatically set, and remains always of egual size, so that economical operation of the refrigeration compressor is possible. This feature is called "economy reheating." In the conventional regulator circuits, such economical operation has not been feasible, since in all cases a proportional cooling power control occurred which was different with respect to the actuating signal. Furthermore, depending on the outside temperature, different transition ranges prevailed depending on the actuating signal. Accordingly, economical operation of the refrigeration compressor was impossible.
It is expedient to regulate the cooling power conventionally by way of activation and deactivation of a refrigeration compressor with a two-position regulator. In this connection, it is advantageous to transmit the output signal of the second amplifier to the input of this two-position regulator by way of a limiter. This limiter prevents preset desired values lower than 0.degree. C. at the two-position regulator and thus precludes icing of the evaporator laminations. It is furthermore convenient to provide that the two-position regulator activates a relay, and the latter activates an electromagnetic clutch which sets the refrigeration compressor into operation.
In an advantageous further development, the temperature of the evaporator can be detected by an evaporator probe, and the signal transmitted by this evaporator probe can be fed back to the input of the two-position regulator. The cooling system in this way forms an independent, closed regulating circuit with desired value modulation.
The output signal of the second amplifier can also be used in an advantageous further development for controlling the position of a fresh air/recirculated air flap. This fresh air/recirculated air flap thus is provided with the same desired value as the cooling system, with the difference that limitation of the desired value does not occur. Control can take place suitably by way of a comparator and a recirculated air relay, wherein the fresh air/recirculated air flap is operated to the position "recirculated air" only during maximum cooling power. Thus, the interior of the vehicle is supplied entirely with recirculated air only when the cooling system has already reached the limit of its capacity.
The heating power regulation can be achieved by controlling water flow. In a preferred embodiment, the regulator consists of a comparator to which is fed the output signal of the input amplifier, and a servo member which is a water valve arranged in the water cycle. At a high desired heating value, this water valve is opened and thus permits unhindered passage of water through the heat exchanger. With the heating system deactivated, the water valve is closed so that hot water can no longer enter the heat exchanger. Another advantageous embodiment provides regulation of the heating power on the air side wherein the regulator consists of a position controller to which is fed the output signal of the input amplifier, and the servo member consists of a servomotor operating a mixing flap. In this arrangement, a feedback potentiometer connected to the mixing flap feeds back a signal corresponding to the position of the mixing flap to the input of the position controller. The mixing flap, in this case, controls the ratio between heated air and unheated air. With the feedback feature, the heating system as well as the cooling system are designed as independent regulator circuits with desired value modulation. An alternative design for the heating power regulation on the air side as well as water side includes the outputs of the regulators which are, for example, pulse sequencers wherein the duration of these pulses or the duration of the pulse intervals is varied.
Additional advantages and features of the invention can be seen from the claims, as well as from the description of the drawings illustrating a preferred embodiment of the invention.